SDD error types and detection

SOFTWARE DESIGN &
DEVELOPMENT
ON LINE WITH
MR CUSACK

LESSON TOPIC
T3W2 – ERROR TYPES & DETECTION

WHAT TYPES OF ERROR ARE THERE?
HINT: THERE ARE 3 TYPES!

ERROR TYPES AND DETECTION
SCENARIO: AFTER USING A SOLUTION FOR SOME TIME USERS REPORT THAT SOME OUTPUTS
ARE NOT AS EXPECTED.

WHAT TYPE OF ERROR ?

WHAT TYPE OF ERROR ?...... LOGIC ERROR

WHY NOT A SYNTAX ERROR ?

WHY NOT A SYNTAX ERROR ?
WHY NOT A RUNTIME ERROR ?

SCENARIO: A PROGRAMMER COMPLETES CODING. SHE ATTEMPTS TO CREATE AN
EXECUTABLE SOLUTION. THIS FAILS.

WHAT TYPE OF ERROR ? SYNTAX ERROR !

DESCRIBE WHAT HAS CAUSED THIS ERROR

DESCRIBE WHAT HAS CAUSED THIS ERROR
AT SOME POINT IN THE CODING THE PROGRAMMER HAS ENTERED CODE THAT DOES NOT COMPLY
WITH THE RULES THAT APPLY TO THIS LANGUAGE. I.E. NOT COMPLIED WITH THE SYNTAX RULES
FOR THAT LANGUAGE.

WHAT IS AVAILABLE TO THE PROGRAMMER TO HELP AVOID THIS ?

METALANGUAGES !

SYNTAX DEFINITIONS AND HELP IN THE FORM OF METALANGUAGES SUCH AS EBNF AND RAILROAD
DIAGRAMS
MESSAGES WITHIN THE PROGRAMMING ENVIRONMENT THAT REPORT SYNTAX ERRORS AND
SUGGEST CORRECTIONS

SCENARIO: A PROGRAM HAS BEEN SUCCESSFULLY RUNNING FOR SOME TIME. A USER
REPORTS THAT THE PROGRAM HAS “CRASHED”.

WHAT TYPE OF ERROR ? RUNTIME ERROR

HOW IS THIS DIFFERENT TO A LOGIC ERROR ?

HOW IS THIS DIFFERENT TO A LOGIC ERROR ?
LOGIC ERRORS USUALLY ALLOW THE PROGRAM TO CONTINUE TO RUN…BUT GIVE
UNEXPECTED RESULTS.
RUNTIME ERRORS CRASH (OR REQUIRE RECOVERY)

WHAT DID THE USER DO THAT MADE THIS HAPPEN ?

WHAT DID THE USER DO THAT MADE THIS HAPPEN ?
PROBABLY ENTERED UNEXPECTED OR INAPPROPRIATE DATA
..OR CREATED EVENTS THAT ARE NOT NORMAL..
..OR WERE NOT ANTICIPATED BY THE PROGRAMMER.

WAS THIS THE USERS FAULT ?

WHAT TYPE OF ERROR ? RUNTIME ERROR. WHAT DID THE USER DO THAT MADE THIS
HAPPEN ?
WAS THIS THE USERS FAULT ?
NO ! THE DEVELOPER SHOULD HAVE ALLOWED FOR THIS POSSIBILITY AND INCLUDED
ADEQUATE TRAPS OR CODE SO THAT THE USER CANNOT CAUSE THIS TO HAPPEN

ERROR TYPES SUMMARY
LOGIC ERRORS
SYNTAX ERRORS
RUNTIME ERRORS

ERROR TYPES SUMMARY
LOGIC ERRORS
SYNTAX ERRORS
RUNTIME ERRORS
HOW CAN THESE BE DETECTED BEFORE THE SOLUTION GOES TO THE CLIENTS ?

LOGIC ERRORS

LOGIC ERRORS
THOROUGH CREATION OF TEST DATA AND DESK CHECKING AT PLANNING STAGE
REPEATING OF THIS TESTING AFTER IMPLEMENTATION

SYNTAX ERRORS

SYNTAX ERRORS
IN MOST PROGRAMMING ENVIRONMENTS THE PROGRAMMING TOOL REPORTS SUCH ERRORS
EITHER AS CODE IS CREATED OR WHEN AN ATTEMPT IS MADE TO TRANSLATE THE CODE.
THESE ARE DETECTED BECAUSE THE PROGRAM WON’T RUN !

RUNTIME ERRORS
(PROBABLY THE MOST DIFFICULT TO DETECT)

RUNTIME ERRORS
AT BOTH THE PLANNING AND DURING IMPLEMENTATION AND TESTING THE DEVELOPER HAS
TO PREDICT WHAT USERS CAN DO AND CREATE TEST DATA SETS TO ENSURE THAT ALL OF
THESE POSSIBILITIES ARE COVERED.

RUNTIME ERRORS
AT BOTH THE PLANNING AND DURING IMPLEMENTATION AND TESTING THE DEVELOPER HAS TO
PREDICT WHAT USERS CAN DO AND CREATE TEST DATA SETS TO ENSURE THAT ALL OF THESE
POSSIBILITIES ARE COVERED.
IN THE CASE OF LARGER SOLUTION RUNTIME ERROR DETECTION
IS OFTEN ACHIEVED BY EXTENSIVE BETA TESTING. IN THIS CASE
MANY USERS ARE ASKED TO RUN THE SOLUTION AND REPORT
BACK PROBLEMS. THIS IS ANOTHER WAY TO HOPEFULLY TEST THE
UNEXPECTED.

AN EXAMPLE
A PROGRAM TO FIND THE AVERAGE OF 5
ELEMENTS IN AN ARRAY

AN EXAMPLE
BEGIN
SET TOTAL TO 0
SET COUNTER TO 1
WHILE COUNTER <5
TOTAL = TOTAL + ARRAY(COUNTER)
INCREMENT COUNTER
ENDWHILE
AVERAGE = TOTAL /COUNTER
END

AN EXAMPLE
BEGIN
SET TOTAL TO 0
SET COUNTER TO 1
WHILE COUNTER <5
TOTAL = TOTAL + ARRAY(COUNTER)
INCREMENT COUNTER
ENDWHILE
AVERAGE = TOTAL /COUNTER
END LOGIC ERROR

AN EXAMPLE
VB CODE
WHILE COUNTER < 5
MAKE THE TOTAL = TOTAL + ARRAY (COUNTER)
ENDDO

AN EXAMPLE
VB CODE…. BEHIND THE AVERAGE BUTTON.
WHILE COUNTER < 5
MAKE THE TOTAL = TOTAL + ARRAY (COUNTER)
ENDDO
SYNTAX ERROR

AN EXAMPLE
A PROGRAM TO FIND THE AVERAGE OF
NUMBERS THAT THE USER ENTERS
LETS ASSUME THAT THE ALGORITHM DESKCHECKED OK
LETS ASSUME THAT THE EXE WAS CREATED OK

AN EXAMPLE
NOW THE USER RUNS THE PROGRAM…SEVERAL TIMES AND IT GIVES CORRECT RESULTS
EVERY TIME

AN EXAMPLE
EVERY TIME
THEN THE USER RUNS THE PROGRAM AGAIN. ENTERS NO NUMBERS AND CLICKS THE
AVERAGE BUTTON

AN EXAMPLE
EVERY TIME
THEN THE USER RUNS THE PROGRAM AGAIN. ENTERS NO NUMBERS AND CLICKS THE
AVERAGE BUTTON
RUNTIME ERROR….DIVISION BY ZERO

FIXING BUGS
SCENARIO: YOU HAVE COMPLETED CODING AND ATTEMPT TO RUN YOUR (LARGE
MODULAR) PROGRAM.
EITHER A RUNTIME OR A LOGIC ERROR IS APPARENT.
HOW CAN YOU FIND AND FIX THE ERROR ?

ERROR DETECTION TOOLS
1. FOCUS ON MODULES.

2. DEBUGGING OUTPUT STATEMENTS

3. STUBS

3. STUBS
4. FLAGS

3. STUBS
4. FLAGS
5. PROGRAMMING TOOLS….BREAKPOINTS, STEPPING, WATCH EXPRESSIONS

AN EXAM QUESTION
A LARGE AND COMPLEX PROGRAM CONTAINS MANY MODULES THAT MANIPULATE DATA.
THE PROGRAM PRODUCES INCORRECT OUTPUT, POSSIBLY AS A RESULT OF CALCULATION
ERRORS IN ONE OR MORE MODULES.
DESK CHECKING THE SOURCE CODE AND PEER CHECKING ARE TWO TECHNIQUES THAT
COULD BE USED TO DEBUG THIS PROGRAM.
DESCRIBE HOW OTHER TECHNIQUES COULD BE USED TO HELP LOCATE THE ERRORS IN THIS
PROGRAM.
HSC 2012

AN EXAM QUESTION
A LARGE AND COMPLEX PROGRAM CONTAINS MANY MODULES THAT MANIPULATE DATA. THE PROGRAM PRODUCES
INCORRECT OUTPUT, POSSIBLY AS A RESULT OF CALCULATION ERRORS IN ONE OR
MORE MODULES.
DESK CHECKING THE SOURCE CODE AND PEER CHECKING ARE TWO TECHNIQUES THAT COULD BE USED TO DEBUG THIS
PROGRAM.
DESCRIBE HOW OTHER TECHNIQUES COULD BE USED TO HELP LOCATE THE ERRORS IN THIS PROGRAM.
YOU COULD USE A PROGRAM TRACE TOGETHER WITH A VARIABLE WATCHER TO
CHECK THE CONTENTS OF VARIABLES AT EACH RELEVANT STEP IN THE PROGRAM –
TO MAKE SURE VALUES ARE CALCULATED CORRECTLY. BREAK POINTS SET IN KEY
SUBROUTINES – IN CONJUNCTION WITH A TRACE – CAN BE USED TO ENSURE THESE
SUBROUTINES ARE EXECUTED AND THAT CRITICAL VARIABLES CONTAIN THE
EXPECTED VALUES AT THESE POINTS IN THE EXECUTION. THE USE OF DEBUGGING
OUTPUT STATEMENTS AND FLAGS WILL ALSO ENSURE THAT THE VARIOUS MODULES
ARE EXECUTED APPROPRIATELY.

1. FOCUS ON MODULES
FIND IN WHICH MODULE THE ERROR OCCURS. DETERMINE WHAT THE USER WAS DOING WHEN THE ERROR
HAPPENED ? THEN FOCUS YOUR DETECTION METHODS ON THAT MODULE.

INSERT TEMPORARY OUTPUTS (LABELS) THAT TELL US THE VALUE OF KEY VARIABLES. REMOVE THESE WHEN
THE ERROR IS FIXED.

THE ERROR IS FIXED.
WHAT WOULD BE APPROPRIATE DEBUGGING OUTPUTS IN THE PREVIOUS AVERAGE
CALCULATOR ?

THE ERROR IS FIXED.
WHAT WOULD BE APPROPRIATE DEBUGGING OUTPUTS IN THE PREVIOUS AVERAGE
CALCULATOR ?
OUTPUT: THE COUNTER, THE TOTAL
TEMPORARILY !

3. STUBS
PARTIALLY COMPLETED MODULES (“UNDER CONSTRUCTION”) THAT TELL US THAT NAVIGATION TO A
MODULE HAS WORKED AND THAT PARAMETERS HAVE BEEN SUCCESSFULLY PASSED. PROGRESSIVELY USE
THESE TO REPLACE MODULES IN ORDER TO ISOLATE THE PROBLEM.

3. STUBS
4. FLAGS
A SIMPLE BOOLEAN VARIABLE THAT RECORDS A “TRUE” WHEN CERTAIN PARTS OF A PROGRAM ARE
ACCESSED OR STATUSES REACHED. OUTPUT THIS AS A DEBUGGING OUTPUT STATEMENT. USEFUL TO SEE IF
CONDITIONS IN SELECTION AND ITERATION HAVE BEEN MET.

3. STUBS
4. FLAGS
5. PROGRAMMING TOOLS….BREAKPOINTS, STEPPING,
WATCH EXPRESSIONS
THESE ARE DEALT WITH IN THE VB EXERCISES.
ESSENTIALLY THESE CAN STEP THROUGH OR STOP EXECUTION…AND DISPLAY THE CURRENT VALUES OF
VARIABLES.
TURNS A BLACK BOX TEST INTO A WHITE BOX TEST.

WHITE BOX TEST:
We see what is changing inside.
We trace the changes in variables.
We know the inputs (test data) and the
expected outputs
Deskchecks when in the planning stage
Breakpoints and debugging output statements
when in the implementation stage

BLACK BOX TEST:
We only know the inputs (test data) and the outputs
We compare these outputs with what is expected.
If actual and expected don’t match…….
We start debugging !

WHEN WE WORK TOGETHER
WE ACHIEVE A LOT
IT’S ALL ABOUT TEAMWORK!

SDD error types and detection

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